Improving bypass performance and passage success of Atlantic salmon smolts at an old fish-hostile hydroelectric power station: a challenging task

Old hydroelectric power stations often provide unsafe migration routes to fish, apart from passing through mobile gates during high flow. The installation of retrofitted bypass is considered be a potential solution improve fish passage at such old structures, but their performances are insufficient. In the Amblève River (Belgium), 3.3 m dam feeds two principal Francis turbines (12 + 14 m3 s?1) and equipped with three gates, modern vertical slot upstream pass downstream functioning very low flow (1% maximum turbined flow). A bypassed river section (length 8.4 km) was set 3 s?1 supplies microturbine. From 2015 2016, we used 1150 hatchery Atlantic salmon smolts (Salmo salar), placed antennae automatic radio-frequency identification (RFID) analyse (n = 5). We tested attraction efficiency performance without placement guidance system entrance examined proportion smolt different under configurations. markedly improved overall efficiency. median time spent 7 12 min, near less than 1 h for 67.1% (release 1), 88.2% 2) 63.7% 3) smolts. During release events, arrived mostly dusk dark periods (87.5%, 96.0% 95.5%, releases 1, 2 3, respectively). configuration opening gate, most route, followed by microturbine main turbine. Stopping gate has consequences making it first choice turbine bypass. re-establishment safe quick holistic view powerstation.